Long Versus Mixed Muscle Length Training On Changes In Elbow Flexors Dynamic Strength

PURPOSE: This study investigated the effect of training with a long muscle length bias (LONG) versus training at both long and short muscle lengths (MIXED) on elbow flexor dynamic strength using a replicated within-subjects design. METHODS: Seven males and females (age 23.00 ± 2.00 yrs; training experience 5.43 ± 2.14 yrs) trained twice per week for eight weeks, underwent a six week washout period, then had limbs re-randomized to conditions and repeated the protocol, effectively doubling the number of observations. In the LONG condition, subjects performed six sets of incline cable curls; in the MIXED condition, subjects performed three sets of incline cable curls and three sets of high cable curls. All sets consisted of 8-12 repetitions to momentary muscular failure. Elbow flexor strength was assessed via 8-12RM on the incline cable curl and high cable curl. To compare changes between LONG and MIXED conditions, a Bayesian linear mixed effects model was constructed with condition, phase, exercise, the interaction between condition and exercise, and the mean-centered pretest value of 8-12RM included as fixed effects, and nested random intercepts at the subject and limb levels to account for multiple observations. Probability density functions were compared to a region of practical equivalence (ROPE) based on measurement error to aid with interpretation. RESULTS: For LONG, a modal increase of 9.1 kg [95% HDI: 4.0, 14.1] and 5.8 kg [95% HDI: 0.3, 10.9] were observed for incline and high cable curl, respectively, with 99.0% and 86.4% probability of exceeding the ROPE. For MIXED, a modal increase of 8.3 kg [95% HDI: 2.9, 13.1] and 7.7 kg [95% HDI: 1.2, 14.0] were observed for incline and high cable curl, respectively, with 97.4% and 93.7% probability of exceeding the ROPE. Modal values for contrasts between conditions were -1.2 kg [95% HDI: -3.6, 1.2] and 2.5 kg [95% HDI: -1.8, 6.0] for incline and high cable curl, respectively, with 83.5% and 12.5% probability of LONG being superior to MIXED, and 9.6% and 39.1% probability of the difference between conditions exceeding the ROPE for incline and high cable curl, respectively. CONCLUSIONS: Changes in elbow flexor strength reflected the principle of specificity, with greater changes in incline cable curl for LONG and greater changes in high cable curl for MIXED.